Fix issue #48 by adding a proper hierarchy model hash implementation.

Author: jturkel

lib/closure_tree/acts_as_tree.rb

@@ -40,6 +40,9 @@ def ==(comparison_object)
           self.attributes == comparison_object.attributes
         end
         alias :eql? :==
+        def hash
+          attributes.hash
+        end
       RUBY
 
       self.hierarchy_class.table_name = hierarchy_table_name

spec/tag_spec.rb

@@ -130,6 +130,15 @@ def nuke_db
         TagHierarchy.find_all_by_ancestor_id(@root.id).should == root_hiers
         TagHierarchy.find_all_by_descendant_id(@root.id).should == root_hiers
       end
+
+      it "should have different hash codes for each hierarchy model" do
+        hashes = TagHierarchy.all.map(&:hash)
+        hashes.should =~ hashes.uniq
+      end
+
+      it "should return the same hash code for equal hierarchy models" do
+        TagHierarchy.first.hash.should == TagHierarchy.first.hash
+      end
     end
 
     it "performs as the readme says it does" do